An interlayer insulating film in which wiring constituting a semiconductor device is embedded is often formed of a low dielectric constant film called a “low-k film”. The low-k film is constituted by, for example, a porous film. Etching is sometimes performed with respect to a semiconductor wafer (hereinafter, referred to as a “wafer”) in which such a porous film is formed in a process of manufacturing the semiconductor device.
For example, there is known a technique for etching a wafer having an interlayer insulating film as a low-k film formed therein to form a recess for embedding wiring. A film is formed in the recess in order to prevent the recess from being exposed to the air until the wiring is embedded in the recess by supplying the film-forming gases. In addition, there is known a technique for etching an organic film embedded in a recess formed in a low-dielectric constant film as a porous film, using plasma of a process gas containing a predetermined amount of carbon dioxide.
In manufacturing a semiconductor device, a process of removing a polysilicon film from a wafer on which the polysilicon film, a SiOCN film as a porous film, and a stacked body of an upper-lying silicon oxide film and an underlying SiGe (silicon germanium) film are formed adjacent to each other in this order in the lateral direction, is sometimes performed. If the removal of the polysilicon film is performed by dry etching, an etching gas may pass through the SiOCN film to thus reach the SiGe film during the etching of the polysilicon film. More specifically, since the SiOCN film is a porous film, the etching gas passes through pores of the porous film from the side of the SiOCN film and reaches the sidewall of the SiGe film. Although the SiGe film is not a target to be removed by etching, the sidewall thereof may be etched by the etching gas thus supplied.
Therefore, for example, a process of removing an upper portion of the polysilicon film by plasma-based anisotropic etching, followed by removing a lower portion of the polysilicon film by wet etching, is performed in some cases. Since the permeability of an etchant used for the wet etching with respect to the SiOCN film is lower than that of the etching gas, etching of the SiGe film is suppressed. However, the multiple operations described above require a lot of labor, and it is impossible to perform the process using wet etching due to the miniaturization of a device. In addition, the thickness of the sidewall of the SiOCN film tends to be reduced. Thus, in the case where the thickness of the sidewall of the SiOCN film is further reduced in the future, the permeability of the etchant with respect to the SiOCN film may be increased, so that the SiGe film may be etched